Electrically heatable nozzle for an injection molding machine, a

Details Electrically heatable nozzle for an injection molding machine, a Electrically heatable nozzle for an injection molding machine, a

1991-08-16

1992-09-29

Heitbrink, Tim

Plastic article or earthenware shaping or treating: apparatus

With upstream screen or perforated plate for straining,...

Plural screens or plates

425549, 425565, 425568, B29C 4520

Patent

active

051510251

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to an electrically heatable nozzle for an injection molding machine, a hot runner system or the like. The nozzle has an inlet opening, an internal chamber and an outlet opening through which molten material, preferably molten plastic, flows.
Nozzles of this type are known (German Offenlegungsschrift 33 35 277) and have a nozzle passage via which the molten material is conveyed to a group of molds. During travel from the production location for the molten material to the group of molds, foreign particles which affect the quality of the molten material and the end product can enter the molten material.


SUMMARY OF THE INVENTION

It is an object of the invention to so design an electrically heatable nozzle of the type indicated at the outset that contaminants resulting from foreign particles can be removed from the molten material, and that these contaminants can be evacuated from the nozzle during a cleansing phase.
According to the invention, this object is achieved in that an annular strainer is placed in the internal chamber of the nozzle and divides the internal chamber into an annular outer compartment and an inner compartment. A switching device is provided and is movable between and arrestable in two terminal positions of which one is designed for the injection procedure and the other for the cleansing procedure. In the one terminal position, the molten material is admitted into the outer compartment and flows through the annular strainer from outside to inside. In the other terminal position, the molten material is introduced into the inner compartment and flows through the annular strainer from inside to outside.
In an advantageous embodiment of the invention, the switching device has a bolt-like control slide whose longitudinal axis coincides with the longitudinal axis of the nozzle and the longitudinal axis of the outlet opening. The servopiston is moved into the terminal position for the cleansing procedure by a switching tube which is introduced into the outlet opening from outside so that the contaminants retained by the annular strainer can be withdrawn via the switching tube.
In this manner, reversal of the control slide becomes very simple. The piston-like end portion of the control slide facing the inlet opening is subjected to the pressure of the admitted molten material which exerts a force on the control slide causing the control slide to move into, or to be held in, the terminal position corresponding to the injection procedure. The control slide is moved into the other terminal position corresponding to the cleansing procedure by the switching tube introduced through the outlet opening. The control slide is held in this terminal position by the switching tube against the pressure of the molten material, and the molten material is conducted through the nozzle in such a manner that it conveys the contaminants accumulated at one side of the strainer to the outside via the switching tube. After removal of the contaminants, the switching tube is withdrawn from the nozzle. The molten material subsequently pushes the control slide into the other terminal position so that the nozzle can again operate in the injection mode.


BRIEF DESCRIPTION OF THE DRAWINGS

An electrically heatable nozzle in accordance with the invention is illustrated in the drawings and is described below.
There is shown:
FIG. 1 a longitudinal section of the nozzle during the injection procedure,
FIG. 2 the nozzle of FIG. 1 together with a switching tube and a mold during the cleansing procedure,
FIG. 3 an elevational view of a guiding disc for the bolt-like control slide,
FIG. 4 a section along the section line IV--IV of FIG. 3,
FIG. 5 a section along the line V--V of FIG. 4,
FIG. 6 the bolt-like control slide,
FIG. 7 a section along the line VII--VII of FIG. 6,
FIG. 8 another guiding disc,
FIG. 9 a section along the line IX--IX of FIG. 8,
FIG. 10 a view in the direction of the arrow X of FIG. 9,
FIG. 11 an elevational view of a strainer disc,
FIG. 12 a section along the

REFERENCES:
patent: 4518501 (1985-05-01), Lenmartz et al.
patent: 4629411 (1986-12-01), Bucheler
patent: 5024763 (1991-06-01), Schlaginhaufen

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